1. Technical Field
The present invention relates to a fryer assembly having an oil stripping capability integral to the unit. More particularly, the invention relates to the extension of the steam collection hood on a chip frying unit and the incorporation of oil stripping features in such extended hood, thereby eliminating the need for a separate low-fat stripping unit.
2. Description of Related Art
Food pieces, such as potato chips, are commonly cooked in hot oil in a fryer, such as a Heat and Control PC-50 fryer. A simplified schematic illustration of such a continuous fryer is shown in FIG. 1.
Referring to FIG. 1, the food pieces, such as potato slices, are inserted into the fryer unit by means of a infeed conveyor 102. The slices then float in the hot oil 104 until removed from the fryer unit by an output conveyor 106. Agitation paddles (not shown) and a submerger 105 can be used to keep the slices from clumping together and floating to the surface of the oil 104. The fried food pieces on the output conveyor 106 are in a bed arrangement, as opposed to single chips in a monolayer arrangement, and are therefore referred to as a product bed 120 on the conveyor 106.
The food pieces are dehydrated during the frying process and, therefore, release moisture in the form of steam. This steam is collected by a hood 108 located above the oil 104. As shown in FIG. 1, it is common to exhaust the steam collected by such hood by one or more large exhaust fans 110 associated with one or more exhaust ports 112, as illustrated by the arrows within the hood 108. The steam temperature within such hood is typically in the range of 220° F. to 260° F., or normally about 240° F. The collected steam from the exhaust ports 112 is typically condensed, collected, and discarded or used in other unrelated processes. Thus, in most prior art applications the latent heat of the steam is essentially lost in the process.
Absent further processing to reduce the amount of oil in the chips produced by the fryer illustrated in FIG. 1, typically potato chips exit such fryer ready for seasoning and packaging with a total oil content by weight of approximately 36% and preferably a moisture level of about 1.1-1.5% by weight. In order to reduce the oil level of such chips, however, the chips can be routed directly from the frying unit illustrated in FIG. 1 by means of the output conveyor 106 to a low-fat stripping unit as illustrated in FIG. 2. This output conveyor 106 remains enclosed such that the fryer of FIG. 1 and the low-fat stripper of FIG. 2 are in communication with each other and each is a part of a single enclosed system.
FIG. 2 is a simplified schematic illustration of a prior art low-fat stripping system or unit, also referred to as a low-fat stripper, such as the model LFSS manufactured by Heat & Controls of Hayward, Calif. Product, such as potato chips, enters the low-fat stripper by means of an infeed conveyor 206, which has received the product from the output conveyor 106 of FIG. 1 or is simply a continuation of said output conveyor 106. The conveyor belt on such infeed conveyor 206 is porous, thereby allowing fluids, such as oil dripping off the product bed 220, to easily pass through the belt. Superheated steam is forced at high velocity through the product bed 220 while the product is on the infeed conveyor 206. This steam strips oil from the surface of the chips. The stripped oil drops to the base of the low-fat stripper or is carried with the steam as it exits the product bed 220.
The steam then flows through an oil separator 222 before being blown through a heat exchanger 224 to be reused again for stripping of the product bed 220. The heat exchanger 224 adds heat to the steam to keep it in a super-heated state. Steam is also constantly generated and added to the low-fat stripper to replace steam vented back to the fryer and lost elsewhere in the system. The steam is circulated throughout the entire unit (as illustrated by the arrows) by a high-volume fan 226. The stripped product exits the unit via an output conveyor 228.
The low-fat stripper recycles some of the steam it uses and removes some of the oil from the product. Potato chips made using a low-fat stripper typically have a finished oil content by weight of between 20% and 28% and a finished moisture level of about less than 2%.
The steam in the low-fat stripper is superheated to typically in the range of 290° F. to 320° F. The pressure in the low-fat stripper unit is maintained at approximately ambient conditions. The velocity of the steam as it blows onto the product bed is in the range of 1,500 ft./min. to 2,500 ft./min. The use of superheated steam in the stripper is important, because if steam at lower temperatures is used the product tends to absorb moisture from the steam. Adding moisture back into the product at this stage is generally undesirable, as it is preferred that the product exit the stripper at or below 2% moisture by weight for, among other reasons, longer shelf stability.
The low-fat stripper, as noted previously, is a separate unit from the fryer illustrated in FIG. 1. As a consequence, a product line that incorporates a low-fat stripper requires a larger plant footprint. In addition, the low-fat stripper is a capital expenditure above and beyond the cost of the fryer itself. There are energy costs as well when steam produced by the fryer is discarded while steam is constantly added and heated in the stripper.
Low-fat strippers such as the one described above require the use of large amounts of steam at very high velocities to effectively strip the product of a meaningful amount of oil. It is now understood that the reason for this high-energy requirement relates to the amount of time that it takes to get the product from the cooking oil 104 of FIG. 1 into the low-oil stripper of FIG. 2. During the transit time from the oil to the stripper, the product cools and continues to absorb oil. One of the mechanisms for reducing the oil in the chip is to heat the chip outside of the oil environment so that the dehydration of the chip drives the expulsion of oil from within the chip and off of its surface. In other words, the continued release of water vapor or steam from within the chip provides a mechanism for removing oil from the chip. When the chip is allowed to cool prior to exposure to superheated steam, much more energy or work is required to remove any substantial amount of oil from the chip. Unfortunately, since the oil stripper and the fryer are two separate units, the transit times between removal from the oil until entrance into the stripper can be in the range of 40 seconds to a minute or more. During that time, the chips cool considerably, making it that much more difficult to remove the oil from the chips.
Consequently, a need exists for combining the low-fat stripper capabilities of reducing the oil content of the finished fried chips with the basic equipment of existing fryers. This new apparatus should minimally affect the equipment footprint of a stand-alone fryer while utilizing the steam produced in situ. Such unit should amount to a decrease in energy usage, decrease in plant footprint, decrease in capital outlay per line, and yet provide finished product chips with a reduced fat content and low moisture content similar to chips produced when an oil stripper unit is used.